Broodies need their own space to keep other hens from interrupting them by laying new eggs in their nests, and also to keep the broody from getting lost on her way back from her breaks and going to set in a different nest.
You can either fence off a space around your broody or move her to a new location. If at all possible, I think it's best to make a barricade around the hen where she is. I like to use the wire tops of guinea pig cages, just place it over the hen in her nest. Or use pieces of wire fencing or boards or whatever. Make sure to give her room to poop, and her own food & water dishes.
If it isn't feasible to do that, then move the hen & her eggs. It's best to do this after full dark, and try to move as much of the nest & even the nest box if you can. My nest boxes are flat-sided feed buckets and if a hen starts to brood in one of those I can simply pick up the whole bucket, hen, eggs & straw at once. If you can't move the nest box, try to slide a sheet of stiff cardboard or a thin piece of wood under the whole nest, to scoop up everything at once.
Some hens are more committed to brooding than others. Some will stick with their eggs no matter where you put them. Others don't handle the change as well, and might stop brooding after they've moved. That's why it helps to do it after dark & to try and keep as much the same as you can.
Most of my broodies are bantams and I seldom let them incubate their own eggs. I let them get started, situate them in their secure location, then swap the eggs they had with other eggs from my standard size hens. I'd rather have more big birds than banties.
If you can't barricade the broody or move her, the next best thing to do is mark the eggs she starts with -- I draw a line all the way around the egg with a pencil -- and then check the nest each night and remove any new eggs that are added.
I wish you & your hens great success, let us know how it turns out!
